The invention relates to a method of producing a mechanically robust star coupler for polymer optical waveguide systems and the apparatus used for it.
A star coupler is an optical component which splits the optical guide in an input fiber into M output fibers. Such components are used in passive optical waveguide networks as optical power splitters. The uniform splitting takes place in the so-called mixed region. Until now, essentially there have been 2 methods of producing star couplers for polymer optical waveguide systems:
1. "Biconical-Taper method" (BT method; cf. K. Imoto et al., Appl. Opt., vol. 25, No. 19, p. 3443 (1986) PA0 2. "Mixing rod method" (MR method; cf. R. D. Codd, SAE/IEEE, International Congress on Transportation Electronics (1984))
In the case of the BT method, a plurality of optical waveguides (glass or polymer) are clustered and stretched under the effect of heat. In the process, a waist having a biconical profile is produced, from which the name of the method derives. Subsequently, the stretched fibers are twisted in the hot zone, so that the optical claddings of the optical waveguides are fused with one another in the waist.
The propagation angles of light rays which are guided in an input fiber become increasingly steep in the tapering region, until the core no longer guides these rays. Beginning with the modes of highest order, core modes increasingly become cladding modes. In the fusion region, the cladding modes of the various fibers mix with one another. When the fibers subsequently separate again, the light rays guided in the cladding are distributed over all of the output fibers and, with increasing fiber thickness, are continuously converted back into core modes.
Star couplers produced by this method are relatively low-loss, but exhibit a strong mode dependence, which in the case of a system structure composed of optical wave-guides, demountable connections and coupler, is taken into account by assuming an overdimensional system reserve.
A further disadvantage of a BT coupler is its mechanical instability in the tapering region, so that use for example in an automobile would not be possible. In addition, production is complex and expensive, since the method only allows one-off production with all the resultant disadvantages, such as for example the inability to reproduce optical parameters.
In the case of the MR method, polymer optical waveguides are adhesively fixed by their polished ends to the end faces of transparent rods or chips. The chips or rods in this case serve as optical mixers.
This method is very complex and expensive in production and therefore not suitable for series production. The optical losses are high.